What are the guidelines for aspirin (acetylsalicylic acid) use in primary and secondary prevention of cardiovascular events?

Aspirin Use Guidelines for Cardiovascular Prevention

Secondary Prevention: Strong Recommendation

For patients with established cardiovascular disease (prior MI, stroke, or revascularization), aspirin 75-100 mg daily is strongly recommended as lifelong therapy after completion of dual antiplatelet therapy. 1

• Aspirin is indicated for all patients with previous myocardial infarction, coronary revascularization, or significant obstructive coronary artery disease on imaging 1
• The dose range is 75-162 mg daily, with 75-100 mg being optimal 1
• For patients with diabetes and established atherosclerotic cardiovascular disease, aspirin 75-162 mg daily is recommended 1
• In secondary prevention, the benefits far outweigh bleeding risks 1

Post-PCI Dual Antiplatelet Therapy

After bare metal stent (BMS) placement, use aspirin 75-325 mg plus clopidogrel 75 mg daily for the first month, then aspirin 75-100 mg plus clopidogrel 75 mg daily for up to 6 months. 2, 1

• For drug-eluting stents (DES): Continue dual therapy for 3-6 months minimum (3 months for -limus stents, 6 months for -taxel stents), then consider continuation to 12 months 2
• After 12 months post-stenting, transition to single antiplatelet therapy with aspirin alone 2
• For patients with aspirin intolerance, clopidogrel 75 mg daily is the recommended alternative 1

Primary Prevention: Age-Stratified Approach

For adults aged 40-59 years with ≥10% 10-year ASCVD risk and no increased bleeding risk, low-dose aspirin (75-100 mg daily) may be considered, but the net benefit is small. 2, 3

Age 40-59 Years

• Consider aspirin only if 10-year ASCVD risk is ≥10% and patient is not at increased bleeding risk 2, 3
• The 2019 ACC/AHA guideline gives this a Class IIb recommendation (may be considered) 2
• The 2022 USPSTF recommends individualized decision-making (Grade C recommendation) 3
• Patients with diabetes aged ≥50 years plus one additional major risk factor (hypertension, dyslipidemia, smoking, family history, or albuminuria) may be considered 1

Age ≥60-70 Years

Do not initiate aspirin for primary prevention in adults aged 60 years or older. 2, 3

• The 2019 ACC/AHA guideline states aspirin should NOT be administered routinely in adults >70 years (Class III: Harm) 2
• The 2022 USPSTF recommends against initiation in adults ≥60 years (Grade D recommendation) 3
• For patients over 70 without established CVD, risks outweigh benefits 1

Absolute Contraindications

Do not prescribe aspirin for primary prevention in patients at increased bleeding risk, regardless of cardiovascular risk. 2

• History of gastrointestinal bleeding or peptic ulcer disease 2, 1
• Age >70 years (for primary prevention) 2, 1
• Thrombocytopenia or coagulopathy 2
• Chronic kidney disease 2
• Concurrent use of NSAIDs, steroids, anticoagulants (warfarin, DOACs) 2, 1
• Uncontrolled hypertension 2, 1
• Clinically active hepatic disease 1
• Age <21 years (risk of Reye syndrome) 1

Bleeding Risk Quantification

• Major gastrointestinal bleeding occurs in 2-4 per 1,000 middle-aged adults over 5 years (4-12 per 1,000 in older adults) 2, 1
• Hemorrhagic stroke increases by 0-2 per 1,000 persons over 5 years 2, 1
• Relative risk of major GI bleeding is 1.6 even with low doses 1

Optimal Dosing

The recommended dose for both primary and secondary prevention is 75-100 mg daily. 2, 1

• In the United States, the most common low-dose tablet is 81 mg 1
• Doses of 75-162 mg daily are acceptable 1
• Higher doses (>100 mg) do not provide proportionally greater benefit but increase bleeding risk 4
• Enteric-coated or buffered preparations do not clearly reduce gastrointestinal adverse effects 2

Special Populations

Hypertensive Patients

For hypertensive patients aged ≥50 years with controlled blood pressure (<150/90 mmHg) and target organ damage, diabetes, or 10-year CVD risk >15%, consider aspirin 75-81 mg daily for primary prevention. 1

• Blood pressure must be controlled before initiating aspirin 1
• Uncontrolled hypertension increases bleeding risk and may attenuate aspirin's cardiovascular benefits 2, 1

Diabetic Patients

For diabetic patients aged ≥50 years with at least one additional major cardiovascular risk factor, aspirin 75-162 mg daily may be considered for primary prevention. 1

• Additional risk factors include: family history of premature ASCVD, hypertension, dyslipidemia, smoking, or albuminuria 1
• Recent meta-analyses show no statistically significant reduction in major cardiovascular events or mortality in diabetic patients without pre-existing CVD 1
• Aspirin is NOT recommended for diabetic patients with asymptomatic peripheral artery disease in the absence of other established CVD 1

Clinical Pitfalls to Avoid

• Do not prescribe aspirin for low-risk individuals: Those with <10% 10-year ASCVD risk derive minimal benefit that is outweighed by bleeding risk 1
• Do not ignore bleeding risk factors: Always assess for history of GI bleeding, concurrent anticoagulation, and uncontrolled hypertension before prescribing 2, 1
• Do not use aspirin as monotherapy for acute coronary syndrome: Dual antiplatelet therapy is required 2, 1
• Do not continue dual antiplatelet therapy indefinitely post-PCI: Transition to aspirin monotherapy after 12 months unless specific indications exist 2